Many aircraft, including most aircraft on long haul and international routes, provide an inflight entertainment (IFE) system. Such systems provide a combination of audio and video entertainment. Modern IFE systems provide passengers with a variety of audio and visual media options, for example, music channels, games, movies, and television programmes. Users can be provided with audio or video-on-demand, meaning that each individual user may select an audio track or audio channel, or an audio-visual programme that they wish to listen to, or watch, at any given time. This is usually achieved by each passenger seat in an aircraft environment having its own visual display unit (usually in the form of an LCD display) and an appropriate jack for receiving the plug for a headset which delivers the audio content to the user. The VDU may be connected to a server directly or through an intermediary device such as a seat electronics box.
Audio from the IFE system is typically delivered to a user through a headset (the terms “headset” and “headphone” are used interchangeable herein). However, the noise generated by the aircraft can be distracting or annoying for the user. Jet engined aircraft tend to generate low frequency noise in and around the 150-200 Hz range. The need to minimise the cost of the headsets precludes the use of dense sound insulating materials which would be required to attenuate noise in this frequency range to any significant degree.
A well-known method of reducing the level of ambient noise apparent to a headset wearer is the technique known as active noise cancellation or active noise reduction (ANR). Here, a microphone mounted to the headset detects the ambient noise. Through suitable signal processing the headset's drivers are driven to produce an inverted (antiphase) version of the signal. The ambient noise and the inverted signal cancel each other, and the user experiences a decrease in the ambient noise level, particularly at low frequencies.
While headphones with integrated active noise cancellation hardware work well, they may be prohibitively expensive to issue to passengers.
Other headphones have sensing microphones which supply a signal to active noise cancellation circuitry provided in the seat i.e. the noise cancellation circuitry is not included in the headset. This reduces the cost of the headset, but even these headsets may be prohibitively expensive to issue to passengers.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge in any country.